In addition to providing telephonic services, wireless telecommunications networks provide a number of supplementary services. One such service is a group call, wherein a member of a predefined group can set up a call to each member of the group. For example, in response to an emergency, a law enforcement dispatcher can notify law enforcement personnel of the emergency using a group call, where the law enforcement personnel and dispatcher are members of a common group.
Services supporting group calls include Voice Broadcast Service (VBS) and Voice Group Call Service (VGCS). VBS allows a subscriber to broadcast a voice call to each of the mobile stations in the group. However, a voice broadcast is entirely a downlink transmission wherein the receiving mobile stations are unable to transmit communications. Voice Group Call Service is a group call wherein each participating member can broadcast to the other members of the group.
Ordinarily, a group call is set up for each member of the group, regardless of their location. Therefore, a group conference could be established in which members are dispersed over a large area, which can be a disadvantage in the situation where the initiator of the group call needs to reach only the members of the group within a certain area. To limit the group call to a particular area, a list of the cells in which members of the group are to be called is maintained by each mobile switching center (MSC). The list of cells are collectively known as the group call area. Members outside the group call area are not called. The list of cells is stored in a database, known as a Group Call Register (GCR) that stores any number of group identification numbers, followed by identifiers of the particular cells in which members of the identified group are to be called.
When a group call is requested to be established by a mobile station belonging to a particular group, the MSC serving the mobile station retrieves the list of cells in the group's group call area. The MSC causes a notification message to be transmitted by a Base Station System over a control channel in each cell of the group call area. The notification alerts the mobile stations of the group call, identifies the group to receive the call, and identifies the traffic channel for the call. Subscribers at mobile stations belonging to the group are alerted and can then receive the group call by tuning to the indicated traffic channel.
Because only cells within a particular group call area receive a group call, handoff procedures for mobile stations engaged in a group call are modified. When a mobile station engaged in a phone call traverses the area of one cell to another cell, the base transceiver station must be changed. To assist in the process, the mobile station periodically measures the signal strengths received from neighboring cells. Information regarding the neighboring cells is provided by a neighboring cell list transmitted to the mobile station from the Base Station System. When the signal strength of a base transceiver station from a neighboring cell exceeds the signal strength from the cell serving the mobile station, the mobile station switches service to the base transceiver serving the neighboring cell. The foregoing has been standardized into a procedure known as Mobile Assisted Handoff (MAHO).
However, when a mobile station is engaged in a group call, the neighboring cell list must be modified. Because cells that are outside the group call area do not receive the group call, a handoff to a cell outside the group call area would disconnect the mobile station from the group call. Therefore, the neighboring cell list must exclude neighboring cells that are outside the group call area. The foregoing is accomplished by removing cells from the neighboring cell list which are not found in the GCR.
Although a particular group call area may be confined to a particular region, and is usually smaller than an MSC/VLR service area, a group call area may include cells of a number of MSC/VLR service areas. For example, a group call area close to a border between neighboring MSC/VLR service areas may include cells within the neighboring MSC/VLR service areas. Therefore, a GCR must not only contains lists of cells that are within the MSC/VLR service area, but must also include cells adjacent to the MSC/VLR service area but within the group call area.
As group call areas are added or expanded, the GCR must be constantly maintained and updated. However, because a GCR must include cells outside the MSC/VLR service area, adding a particular cell to a group call area can require several GCRs to be updated to include the added cell in the group call area. Updates to a GCR can be performed manually by an operator. However, as an increasing number of changes occur, manual changes by an operator become tedious and error-prone.
Accordingly, it is an object of the present invention to provide a mechanism to more efficiently update group call registers with changes in group call areas.